1. Field of the Invention
The invention relates to a brake control device that controls the braking force applied to wheels provided in the vehicle.
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-2006-123889 describes a hydraulic brake device that includes a hydraulic pressure booster, a master cylinder, a power hydraulic pressure source, and a plurality of brake cylinders. According to this hydraulic brake device, the brake cylinders are selectively connected in communication with the hydraulic pressure booster, the master cylinder and the power hydraulic pressure source through the use of a simple circuit, so that the controllability can be improved. When the system is normal, the working liquid is supplied from the power hydraulic pressure source to the brake cylinders. If an abnormality is detected, the control mode is switched to a control mode that is different from the control mode selected during the normal state. At the time of switching the control mode, a plurality of control valves provided within the brake device are altered in the open-closed state.
Furthermore, Japanese Patent Application Publication No. JP-A-10-16752 describes a brake fluid pressure control device. In this device, if an excessive wheel cylinder pressure occurs on a wheel cylinder, the wheel cylinder is connected for conduction to a reservoir tank so as to reduce the wheel cylinder pressure. Then, at the time point when the wheel cylinder pressure is appropriately reduced, the master cylinder and the wheel cylinder are connected for conduction. Therefore, even though the hydraulic pressure source of the wheel cylinders is switched to the master cylinder, the high liquid pressure does not reversely flow from the wheel cylinders of the master cylinder.
Depending on the site of occurrence of an abnormality, there is possibility that fluid pressure may be confined in a wheel cylinder due to the switching of the control mode. If the confinement of wheel cylinder pressure occurs, a corresponding one of the wheels is caused to have a drag.